The present invention relates to an inkjet printing apparatus and image data generation method of said apparatus, and more particularly, to an inkjet printing apparatus and image data generation method of said apparatus, which can effectively prevent occurrence of cockling while performing printing with an inkjet printhead which discharges ink based on information transmitted by an external apparatus.
A printing apparatus serving as a printer, copying machine, facsimile apparatus or the like, or a printing apparatus serving as an output apparatus of a work station or composite electronic device including a computer or word processor or the like, is configured to print an image on a print medium, such as paper or a plastic sheet, based on image data. Printing apparatuses of this type are categorized by the printing methods they adopt: an inkjet method, wire-dot method, thermal method, laser method and so on.
An inkjet printer adopting the inkjet method performs printing with the use of a printhead serving as printing means, which discharges ink on a print medium. The inkjet printer has the following advantages: easy to downsize printing means, the ability to print high-definition images at high speed, ability to print on regular paper without requiring special processing, low running cost, low-noise operation because of its non-impact method, easy to print color images with multiple colors of ink, and so forth.
Particularly a printhead having high-density fluid passages (discharge orifices), employed in the inkjet method for discharging ink by utilizing heat energy, can easily be manufactured by the semiconductor manufacturing processes of etching, deposition and sputtering. Therefore, the entire printing apparatus can be further downsized. In the similar sense, a printing apparatus adopting the thermal method can be further downsized similar to the inkjet printer.
The recent trend in such inkjet printer is a system in which a host apparatus transmits a printing command to a printer in the page description language (PDL) so as to share the transmitting data irrespective of the resolution of printers.
Steps of generating printing image data to be used in printing based on an image drawing command written in the PDL are described with reference to the block diagram in FIG. 5. An image drawing command 501, transmitted by the host computer, is transferred to the inkjet printer through a communication cable or the like. The inkjet printer interprets and processes the received command at a command interpretation unit 502 to generate various printing image data, and stores the generated data in image memory 510.
The image drawing command 501 represents a group of image drawing commands. FIG. 6 shows the format of each command. Each image drawing command consists of image shape information 601, image position/size information 602, image density information 603, and fill-in information 604. The image shape information 601 indicates a shape, such as a circle, square, and so on. The image position/size information 602 indicates, for instance if the image is a circle, X and Y coordinates of the center and the radius of the circle. The image density information 603 indicates a color, e.g., red, blue, or green, and density thereof in a specified range (e.g., 0 to 255). The fill-in information 604 indicates whether or not the image is just a line of circle with no fill-in patterns or a circle whose circumference and inside the circle are filled in.
Among these information, the image shape information 601 and image position/size information 602, which are related to the image drawing position, are processed by an image shape interpretation unit 503, then the drawing position is determined by an image position interpretation unit 504, and outputted by a memory control unit 505 as the memory address information of actual image memory 510. Meanwhile, the image density information 603 is subjected to xcex3 conversion, which is unique to the printing apparatus, by an image density conversion unit 507, and outputted as color data of the image to the image memory 510. A fill-in control unit 506 interprets the fill-in information 604 to determine existence/absence of filled-in areas, and controls a value outputted to the image density conversion unit 507 based on the information of the memory control unit 505.
In inkjet printers, there is an important relation between print paper and the amount of ink droplets discharged per unit area (also called a discharge amount).
When a large amount of ink droplets is discharged onto print paper, cellulose which constitutes paper swells in the print paper. In particular, when ink having a characteristic of low permeability into print paper is used, the ink droplet discharged by a printhead hardly permeates through the print paper, thus remains on the print paper surface. As a result, the aforementioned phenomenon of cellulose swelling takes place only on the face of the print paper surface, resulting in different surface areas on the face and back of the print paper. Ultimately, a corrugation phenomenon, called cockling, occurs in the portion of the print paper surface on which a large amount of ink droplets is discharged. Furthermore, in a case where a large amount of ink droplets is discharged on the entire page of print paper, a curling phenomenon of the print paper takes place.
When the cockling phenomenon occurs, the spaces between print paper and a printhead become unstable. Variations of the ink droplet discharging direction cause to lose stability in the ink droplet discharging position on the print paper surface, resulting in image quality deterioration. Furthermore, when the curling phenomenon occurs, it is difficult to align print paper in case of printing plural pages, imposing inconvenient handling. In addition, the curling phenomenon can cause snagging of paper or malfunction in the printer.
In order to prevent the above-described cockling or curling, methods have been proposed to limit the ink discharge amount based on actual printing image data or halftone image data, which is the pre-stage data of the actual printing image data.
However, according to the proposed methods, data processing must be performed on each pixel data. Therefore, processing a high-resolution image increases the number of times of operation. This processing requires hardware with high processing speed, and also is time consuming. Furthermore, it is difficult to control the ink discharge amount in accordance with each print medium used.
The present invention has been proposed to solve the conventional problems, and has as its first object to provide an inkjet printing apparatus, which can effectively prevent the occurrence of cockling without largely increasing a load imposed upon hardware.
The second object of the present invention is to provide an image data generation method of the inkjet printing apparatus, which can effectively prevent the occurrence of cockling without largely increasing a load imposed upon hardware.
Another object of the present invention is to provide a computer program and storage medium storing the program, which implements the image data generation method of the inkjet printing apparatus.
According to the present invention, the first object is attained by providing an inkjet printing apparatus for printing on a print medium based on a drawing command with the use of an inkjet printhead for discharging ink, said apparatus comprising: calculation means for calculating an area of a graphic to be drawn based on the drawing command; first determination means for determining whether or not the calculated area exceeds a predetermined value; second determination means for determining based on the drawing command whether or not a density value of the graphic exceeds a predetermined density value; and density conversion means for converting the density value in accordance with determination results of the first and second determination means.
Furthermore, according to the present invention, the second object is attained by providing an image data generation method for generating image data for printing on a print medium by an inkjet printhead for printing by discharging ink, said method comprising: a calculation step of calculating an area of an image to be drawn based on the drawing command; a first determination step of determining whether or not the calculated area exceeds a predetermined value; a second determination step of determining based on the drawing command whether or not a density value of the image exceeds a predetermined density value; a density conversion step of converting the density value in accordance with determination results of the first and second determination steps; and an image data generation step of generating the image data based on the converted value.
In other words, according to the present invention, in an inkjet printing apparatus for printing on a print medium by an inkjet printhead for discharging ink, when image data is generated based on a drawing command, an area of a graphic or an image to be drawn is calculated based on the received drawing command, and it is determined whether or not the calculated area exceeds a predetermined value, and whether or not a density value of the graphic or the image exceeds a predetermined density value based on the drawing command. In accordance with the two determination results, the density value is converted, and image data is generated based on the converted value.
According to the foregoing configuration of the present invention, image data to be used in printing is generated by reducing a density value of a portion having a high probability of cockling occurrence, based on information included in an inputted drawing command. Therefore, quick image data generation is realized without largely increasing a load imposed upon hardware. Furthermore, cockling or curling can effectively be prevented without deteriorating print quality.
Note that it is an aspect of the invention that the density value is converted when it is determined that the calculated area exceeds the predetermined value and the density value exceeds the predetermined density value.
Further, it is an aspect of the invention that the density value is reduced at a predetermined rate in the density conversion.
Still further, it is an aspect of the invention that the predetermined value and predetermined density value can be changed. For instance, to perform printing suitable to each type of print medium, the predetermined value and predetermined density value are changed in accordance with the type of print medium used.
Similarly, it is also effective to change the predetermined rate in accordance with the type of print medium used.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.